A communication system can be seen as a facility that enables communication between two or more entities such as user equipment, elements of a communication network and other entities associated with a communication system. A communication system typically operates in accordance with a given standard or specification which sets out what the various entities associated with a communication system are permitted to do and how that should be achieved. For example, the standard specification may define if a user, or more precisely, user equipment or a terminal is provided with a circuit switched service and/or packet switched service. Communication protocols and/or parameters which shall be used for the connection may also be defined. In other words, a specific set of rules, in which the communication can be based needs to be defined to enable communication by means of the system.
Communication systems providing wireless communication for the user equipment are known. There are various known standards or proposals for standards including GSM (Global system for mobile communication), UMTS (universal mobile telecommunications system) and others. An example of a wireless is a cellular network. In cellular systems, a base transceiver station (BTS) or similar access entity serves mobile station (MS) or other such wireless user equipment (TIE) via a wireless interface between these entities. The communication between the mobile stations and the elements of the communication network can be based on appropriate communication protocol. The operation of the base station apparatus and other apparatus required for the communication can be controlled by one or several control entities. The various control entities may be interconnected. One or more gateway nodes may also be provided for connecting the cellular network to other networks. The other networks may comprise, for example, another mobile network, a public switched telephone network (PSTN) and/or other communication networks such as an IP (Internet Protocol) and/or other packet switched networks.
An example of a service that may be offered to the subscribers of a communication system is a so called multimedia service. An example of a communication system which is enabled to offer the multimedia services for the users is an IP (Internet Protocol) multimedia network. IP multimedia (IM) functionalities can be provided by means of an IP multimedia sub system (IMS). The data to be communicated in the multimedia application may comprise various types of data. For example, voice, video or other image data, streaming data, text data and other content data may be communicated via a communication system.
A multimedia application is the so called multimedia broadcasting multicasting service (MBMS). The MBMS can be described as a multimedia service that is arranged to transmit MBMS data to users which request the service by means of a point to point (P-t-P) and/or point to multipoint (P-t-M) connections. The multimedia broadcasting multicasting services can be divided into two modes—a broadcast mode and a multicast mode.
A broadcast service is a unidirectional point to multipoint service in which data is transmitted from a single source (for example a base station) to multiple user equipment in an associated broadcast service area. Broadcast services may be received by all users who have enabled the specific broadcast service locally on their user equipment and who are in the broadcast area defined for this service. In general, the mobile station is able to receive the MBMS data without any request for the services. The broadcast mode may use radio/network resources for transmission of data over a common radio channel.
The multicast services is a uni-directional point to multipoint service in which data is efficiently transmitted from a single source to a multicast group in the associated multicast service area. Multicast services can only be received by such users that are subscribed to the specific multicast services and have joined the multicast group associated with the specific service. The definitions of the broadcast service and multicast service are defined in the UMTS third generation partnership project specification number 3GPP TS 22.146, which is hereby incorporated by reference.
As with the broadcast mode, data may be transmitted via radio/network resources over a common radio channel. The multicast mode provides the possibilities for selective transmission to cells within the multicast service area. The selective cells contain members of a multicast group. A multicast service received by user may involve one or more successive multicast sessions. A multicast service might, for example, consist of a single on going session such as a multimedia stream. The multicast service may involve several intermittent multicast sessions over an extended period of time, for example messages to users.
A difference between the two MBMS modes is that in the broadcast mode all users within the service area are targeted whereas in the multicast mode it is possible to limit the number of target users, for example to predefine a subset of users in the service area. Furthermore, the modes differ in that in the broadcast mode there is no specific requirement to activate or subscribe to the MBMS.
In current proposals, the MBMS coverage in a cell is defined on certain presumptions of the user distribution in the area of the cell coverage i.e. only intended for part of the full service area. In reality, the distribution of the users can vary so that sometimes, the relevant users will be located close to the base station or the users will be at the cell boarder. As the MBMS service is transmitted with a point to multipoint connection, the output power of the BTS of the MBMS data channel is selected on the basis that a user at the edge of the cell should be able to receive the MBMS data channel with a certain quality of service.
Furthermore, the output power selected for the base transceiver station also is generally based on an assumption that there is a particular level of usage (and hence interference) of the cell. The inventors have realised that the base transceiver station, given the loading of the cell and the location of the users might be transmitting with an unnecessarily high output power.